HVAC-Talk site will be slow for the next few days. It's normal site/server maintenance. Thx -Dad

Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

multi-city units

I need to recover and weigh in the charge on 3 city multi units tomorrow. Is there a way to pump the systems charge into the condenser to make recovery easier? What would be the best way to do this job. thanks

I haven't had much experience with the city multi units. I would suggest calling Mitsubishi tech support with any questions regarding these systems. 678-376-2900. You may also be able find information @ www.mylinkdrive.com.

Mitsubishi isn't very helpful unless you've been to their seminar or your company is approved or certified or whatever they call it. On the last few we've done we've removed refrigerant to a recovery cylinder and weighed back in from there. No special technique.

well, i recoverd two units today. the first was 20 pounds over charged the second was 33 pounds under charged pulled a vacuum on that one and it was holding for about an hour, pressurized it to 500 psi with nitrogen till monday. i hope it holds. dont really want to leak check this mess

How did your units get overcharged or undercharged? I just finished installing 3 citymulti units they made me measure my liquid line by length and size so they can provide me with the amount of refrigerant needed. We kinda got it easy though my company hasnt sent any techs to get the start up training. So Mitsubishi did the start up for us on all three units. So far ive had nothing but luck with these units. 3 years ago i installed 2 citymulti units and never had one service call.

I have installed 3 of the City Multi systems- a great tip is to inventory your refrigerant tubing (lengths) & save the unused pieces from each branch line. Measure those left over pieces & subtract to get a very accurate line length. I have use this method & weighed in charge, have never had any issues on any of the jobs. Oldest system still working installed in 2004! These are great systems only if installed properly, follow good refrigeration practices & they'll be very dependable.

Mini's, including single head, multi-head, and systems designed for many multi-heads... are ALL--VERY sensitive to charge... it is part of how they work. The 'rule of thumb' stuff we did/do with conventional split systems does NOT work.

Cleanliness is important!

Hmmm... I realize we are talking about a large amount of refrigerant... however if many folks have worked on the system... do we have any way to know if it has been contaminated with N2, air, wrong refrigerants, poor vacuum procedures, etc? If it were me, I would sell the owner on NEW refrigerant. If so, standard practices of cleanliness in leak check and triple evac would be my approach.

If you are going to re-use the refrigerant: Pull a vacuum on a CLEAN recovery cylinder. When you start to pull your charge, flush out your hoses, gauge set, cooling coil, etc. Be sure ONLY refrigerant gets into the recovery cylinder. I would err on the side of releasing a 'deminimus amount' of refrigerant... rather than chancing any inert gasses. Pull the charge down to almost zero. \
At this point do your leak check if you are going to.
Then carefully pull a thorough vacuum to specs. I go for at least 250 Microns most of the time. Remember to measure your microns at the unit, not at the gauge set or pump.

CAREFULLY calculate the charge and recharge... being careful your scale is not affected by things like hose weight and bumping.
ACCURACY is the most import thing here...

Been through the City Multi training course. They have a design program where you "build" your system with available components. It will give you exact weigh in charge and liquid and suction line sizes. I like to recover, and weigh in virgin refrigerent.
Also, if you want to troubleshoot a city multi system, you will need the mitsubishi "box" and a laptop, and place your clips on the data circuit between components. The "box" is pricey, I think about $400. The rig will give you the diagnosis.

If your concerned about a leak best bet it to focus on BC controller flare fittings will leak if a torque wrench is not used. If isolation valves were used at BC check schrader cores. Most checks I find oil present.